Rad17 recruits the MRE11-RAD50-NBS1 complex to regulate the cellular response to DNA double-strand breaks

The MRE11-RAD50-NBS1 (MRN) complex is essential for the detection of DNA double-strand breaks (DSBs) and initiation of DNA damage signaling. Here, we show that Rad17, a replication checkpoint protein, is required for the early recruitment of the MRN complex to the DSB site that is independent of MDC1 and contributes to ATM activation. Mechanistically, Rad17 is phosphorylated by ATM at a novel Thr622 site resulting in a direct interaction of Rad17 with NBS1, facilitating recruitment of the MRN complex and ATM to the DSB, thereby enhancing ATM signaling. Repetition of these events creates a positive feedback for Rad17-dependent activation of MRN/ATM signaling which appears to be a requisite for the activation of MDC1-dependent MRN complex recruitment. A point mutation of the Thr622 residue of Rad17 leads to a significant reduction in MRN/ATM signaling and homologous recombination repair, suggesting that Thr622 phosphorylation is important for regulation of the MRN/ATM signaling by Rad17. These findings suggest that Rad17 plays a critical role in the cellular response to DNA damage via regulation of the MRN/ATM pathway. Synopsis The DNA damage sensor protein RAD17 contributes to ATM activation by mediating early, MDC1-independent recruitment of the MRE11-RAD50-NBS1 (MRN) complex to DNA double-strand breaks. A positive feedback loop via ATM-dependent RAD17 phosphorylation facilitates an immediate and effective cellular response to DNA damage. RAD17 interacts with NBS1 following DNA double-strand break induction. RAD17 facilitates early recruitment of the MRN complex to DNA double-strand breaks. RAD17 phosphorylation at Thr622 by ATM is important for NBS1 interaction, MRN recruitment, and activation of ATM signaling. Rad17 promotes ATM activation in a positive feedback loop. Rad17 phosphorylation at Thr622 is important for efficient homologous recombination repair. The DNA damage sensor protein RAD17 constitutes an unexpected MDC1-independent mechanism for early recruitment of ATM-activating MRN complexes to DNA double-strand breaks.